Mixers are often used in radio frequency (RF) systems and microwave systems to down or up convert RF signals to an intermediate frequency (IF) signals. U.S. Pat. No. 7,880,557, incorporated by reference herein, discloses a double balanced mixer which may utilize a hybrid balun; U.S. Pat. No. 5,060,208, incorporated by reference herein, discloses monolithic double balanced mixer which may employ an active distributed element balun; U.S. Pat. No. 6,653,885, incorporated by reference herein, teaches an on-chip integrated mixer with a balun circuit; U.S. Pat. No. 5,361,409, incorporated by reference herein, discloses a FET mixer which requires low local oscillator power levels and high third order intercepts; and U.S. Pat. No. 7,580,693, incorporated by reference herein, teaches a passive reflection mixer, such as a single, double, or triple balanced mixer that utilize FETs.
Active mixers typically rely on analog circuitry to produce the IF signal while passive mixers typically utilize switching transistors to create the IF signal.
In either case, the IF frequency may be achieved by injecting a local oscillator (LO) signal into the mixer with a LO driver circuit. The LO driver circuit needs to provide a sufficiently large constant peak-to-peak voltage swing at the LO inputs to the mixer to obtain good high third order intercept point (IP3) and conversion gain. The large constant peak-to-peak voltage swing at the LO inputs is difficult to achieve over broad frequency ranges using conventional LO driver circuits. In order to maintain the needed peak-to-peak voltage swing, conventional LO driver circuits are often inductively loaded with a single pair of inductors, or a center tapped transformer, with series D-Q resistors to define the low frequency gain and overall bandwidth. However, parasitics associated with the switching devices and the inductors reduce the output impedance and corresponding peak-to-peak gain of the LO driver circuit as the input frequency increases. As a result, conventional LO driver circuits may have poor swing behavior of the voltage at the LO inputs to the mixer as the LO frequency increases. Additionally, as the voltage swing at the LO inputs to the mixer changes with frequency, conventional passive mixers often rely on changing the control voltage of the mixer for each frequency to obtain the best IP3 and conversion gain. Such a technique is cumbersome and requires interaction by a user.